If the null hypothesis is confirmed statistically (that is, not rejected), the instruments pass the test; they are valid by this criterion.
In the Shi and Svensson working paper (which shows that elected national governments in 1975-1995 had larger fiscal deficits in election years, especially in developing countries), the Sargan statistic was asymptotically distributed chi-squared if the null hypothesis were true. (Econterms)
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